Most modem-day wars are fought in urban environments. Large cities and small towns are the battlegrounds of choice by many present-day enemies. Unfortunately, this environment allows opponents to hide in numerous structures and amongst non-combatant civilians. These environments also provide a much harder and more complicated war to fight than existed in many previous conflicts. In simple terms, one reason for this is that walls tend to get in the way of today's battlefield communications and sensor technologies. One solution to this major new U.S. military problem lies in the time-honored profession of human reconnaissance and surveillance, especially with respect to enemy encounters that involve battles in urban neighborhoods. Unfortunately, it may take years before the United States can develop a capability to successfully gain information regarding this new type of enemy.
Consequently, there is little alternative except to approach a complicated problem with the use of high-technology systems, systems such as satellites and unmanned aerial vehicles, UAV's used for surveillance purposes. Such systems may include silent, battery-powered, mini and micro-UAVs, i.e., silent unmanned aerial vehicles. Limited battery energy is however currently a major technological hurdle for all-electric silent unmanned aerial vehicles making them unsuitable for most urban battlefield environments. Using today's “off-the-shelf” secondary battery technology, a silent unmanned aerial vehicle (depending on aerodynamic capability and DC motor size) can perform for at most, 60 minutes out in an urban environment. This capability is of course consumed over the time it takes for the silent unmanned aerial vehicle to make a round trip away from and back to a base i.e., i.e., half of the silent unmanned aerial vehicle's energy is lost on the return trip to base. From a differing perspective, this limited capability additionally means a silent unmanned aerial vehicle-using military unit must be located sufficiently close to an urban area to make the unmanned aerial vehicle effective as a surveillance tool. These considerations presently make current silent unmanned aerial vehicle technologies quite limited for real-time urban military operations.
At first blush one might be tempted to make a silent unmanned aerial vehicle smaller and lighter and thus decrease the level of the required propulsion energy. Unfortunately, however there are very severe physics limitations to the methodology of shrinking an unmanned aerial vehicle both in size and weight. Doing so creates a much more serious mission-capability dilemma in that as the size and weight of the unmanned aerial vehicle decreases, its payload capacity decreases not linearly, but exponentiallyi! (Numbers of this type refer to the list of publications at the end of this specification.) Also, the aeronautical equations dependent on a “Reynolds” number are not usable for small air vehicles of, for example, less than 18 inches in size. Thus use of current-off-the-shelf (COTS) aeronautical CAD software to help design silent unmanned aerial vehicles of these sizes is not possible and one has no recourse but to “guess” a solution and hope it flies. This situation is worsened more by the fact that various aerodynamic instabilities are magnified as the vehicle size decreasesii. This particular problem can be seen in nature while small birds are landing or fighting-off gusts of wind. These birds have to flex and twist their wings and tails to compensate for instantaneous instabilities. Thus it may be appreciated that making electric UAVs smaller presents several technological obstacles.
As a result of these difficulties, existing and pending electric silent unmanned aerial vehicles are useful for only very limited DoD missions. Moreover the personnel that use operate and maintain these vehicles must resign themselves to the fact that the battery-power problem is an existing limitation that unfortunately must be factored into the performed mission. Although a new battery technology offering significantly improved energy storage density may ultimately change this picture, it appears likely that this will not occur soon. If laptop computers are used for comparison, in view of their use of similar rechargeable batteries, it may be observed that over the last decade, battery technologies have barely progressed, progressed not nearly as rapidly as other computer related devices such as CPU speed and RAM capacity. In a similar vein of thought the electrically driven automobile is now being approached with use of hybrid electrical motor and fuel driven engine arrangements and with fuel cells but in a large part awaits the availability of rechargeable batteries of suitable energy storage density before becoming widely used.
The present invention is believed to offer at least a partial solution to these difficulties and to make the silent unmanned aerial vehicle a bit closer to being of practical value especially in a military environment. Theoretically silent unmanned aerial vehicle units made according to the present invention can operate in an urban field for an indefinite time interval (i.e., 24/7/365 capability) with infrequent “return-to-base” cycles being required. Most importantly this long term performance is available with use of presently available technology including present day secondary batteries.
The prior art shows numerous uses of inductively coupled electrical energy, energy coupled by way of a magnetic field rather than by electrical circuit continuity. These uses include for example the electric toothbrush, electrical measuring instruments and cellular telephones in the small energy quantity range and extend to submersible vehicles and other propulsion and underwater applications in the larger energy quantity range. These uses and others are included in the several prior art patents identified in the disclosure statement filed with the application of the present patent document the contents of these issued patents is hereby incorporated by reference herein. None of these energy transmission inventions appear however to have involved an airborne surveillance vehicle or the possibly surreptitious or clandestine acquisition of inductively coupled electrical energy found in the present invention.